MathJax tends to me more forgiving about syntax errors than latex. This guide will cover several common issues. The documentation infrastructure is in continuous development, so support or workarounds may become available in the future.
Good locations to test equations for both latex and MathJax:
The \mathbold command is not supported.
Red highlighting is currently unsupported.
Hints on the use of \eqnarray:
\mbox{} may require surrounding braces as in {\mbox{}}& you must use eqnarray\) within \mbox{}
\mbox{nonpen\_SW}\mbox{nonpen}\_\mbox{SW}MathJax automatically switches to text mode within an mbox{}. If you need to
embed a formula within an mbox{} escape it with a $.